DHAHRAN, SAUDI ARABIA, SEPT. 30 -- Two U.S. airmen were killed today when their F-15 fighter jet crashed in the southern Saudi desert during what officials called a routine exercise flight.

They were the second and third Air Force servicemen reported killed in Saudi Arabia since the beginning of Operation Desert Shield nearly two months ago. A U.S. F-16 fighter crashed in the desert Sept. 3, but the pilot bailed out and was not hurt.

Air Force officials said the two officers aboard the F-15 were assigned to the 4th Tactical Fighter Wing, but they declined to identify them further pending notification of their families.

The crash brought to at least four the number of U.S. servicemen killed in the Persian Gulf region during the U.S. military buildup here. An Air Force staff sergeant was hit by a truck while directing traffic on a darkened runway, and a U.S. seaman was electrocuted aboard a warship plying gulf waters. Five crewmen were injured in the crash of an Army UH-60 Blackhawk helicopter in Saudi Arabia Saturday, and one remained in critical condition today, officials said.

Thirteen servicemen, mostly reserves from Texas, were killed Aug. 29 at Ramstein Air Base in West Germany when a C-5A cargo plane ferrying supplies to the gulf crashed on takeoff.